In 1904, the new church was dedicated and parishioners were under the care of the Jesuit fathers. In 1929, diocesan priests assumed the pastoral duties so that the Jesuits could devote their energies to education.
The Italianate structure was designed by Williams and Clark and built of brick. The roof and twin towers were of wood and are capped by gold cupolas. There were slender Romanesque windows and a rose window, all of stained glass. Inside, frescos painted by the Jesuits adorned the ceiling. The wood communion rail, pulpit, and altar were carved by hand. The 22 statues are from the period 1890-1020.
Originally, the parish served families of the wealthy neighborhood of First Hill. The seating capacity of 950 made it the largest assembly hall in Seattle at the time. As the neighborhood changed, it served an ethnically diverse population of the inner city.
On January 10, 1977, the Seattle City Council designated Immaculate Conception a Seattle Landmark because of its significance in the development of the city, because it exemplified the heritage of the community, and because of its distinctive architectural style.
The church was damaged by a fire in 1982 and restoration was handled by Bumgardner Architects.